1. Field of Endeavor
The present invention relates to gas turbines, and in particular to axial flow gas turbines.
2. Brief Description of the Related Art
The invention relates to an axial flow gas turbine, an example of which is shown in FIG. 5. The gas turbine 10 of FIG. 5 operates according to the principle of sequential combustion. It includes a compressor 1, a first combustion chamber 4 with a plurality of burners 3 and a first fuel supply 2, a high-pressure turbine 5, a second combustion chamber 7 with the second fuel supply 6, and a low-pressure turbine 8 with alternating rows of vanes 13 or 33 and blades 16 or 36, which are arranged in a plurality of turbine stages arranged along the machine axis 9.
The gas turbine 10 according to FIG. 5 includes a stator and a rotor. The stator includes a housing with the vanes 13, 33 mounted therein; these vanes 13, 33 are necessary to form profiled channels where hot gas developed in the combustion chamber 7 flows through. Gas flowing in the required direction hits against the blades 16, 36 installed in shaft slits of a rotor shaft and causes the turbine rotor to rotate. To protect the stator housing against the hot gas flowing above the blades 16, 36, stator heat shields installed between adjacent vane rows are used. High temperature turbine stages require cooling air to be supplied into vanes, stator heat shields and blades.
A section of a typical cooled gas turbine stage TS of a gas turbine 10 is shown in FIG. 1. Within a turbine stage TS of the gas turbine 10, a row of vanes 13 is mounted on a vane carrier 11. Downstream of the vanes 13 a row of rotating blades 16 is provided, each of which has an outer platform 17 at its tip. Opposite to the tips of the blades 16, stator heat shields 18 are mounted on the vane carrier 11. Each of the vanes 13 has an outer platform 14. The vanes 13 and blades 16 with their respective outer platforms 14 and 17 border a hot gas path 12, through which the hot gases from the combustion chamber flow.
To ensure operation of such a high temperature gas turbine 10 with long-term life span, all parts forming its flow path 12 should be cooled effectively. Therefore, cooling air 23 is directed through respective cooling bores 21 and 22 from a plenum 20 to the stator heat shields 18 and vanes 13 and hot outer platforms 17 of the blades 16. However, the known turbine design of FIG. 1 requires sufficient additional amount of cooling air 23 to be supplied into a cavity 19 on the back of the stator heat shields 18 to cool those stator heat shields and the outer blade platform 17, and this feature can be considered as a shortcoming of this design. Another drawback is the traditional way of stator heat shield fixation, where a gap exists between a vane 13 and the stator heat shield 18 (see the encircled zone A in FIG. 1), and a portion of cooling air leaks from the cavity 19 through that gap into the turbine flow path 12 (see arrows in the zone A).